I'm trying to automate access to a website via scraping, and I'm trying to determine what parameters are being sent to the server in a POST request. I've currently got Wireshark open, but is there a better way to do this? Will I be able to see my POST request in plaintext, since the connection is HTTPS?
If you are using Firefox als your HTTP-client there's the option to use the "Tamper Data" AddOn to investigate your HTTP POST requests (and even replay them with an editable set of data).
Use Fiddler2. It acts as a proxy and will basically perform a man-in-the-middle attack to sniff HTTPS. You'll get a cert error, but that's fine.
EDIT: It also works for more than just web traffic.
The wireshark wiki has a link on how to decrypt SSL traffic with wireshark. That requires control on the certificate that the client uses, though, not sure it applies to you.
My favorite Firefox extension is Live HTTP Headers. You can either capture live headers as various HTTP requests are made, and open up page info and look at the headers for the current page that was loaded. In addition to showing both all request and response headers, it also show the contents of a POST body.